1. Field of Invention
The present invention relates to inductor fabrication on a semiconductor substrate. More particularly, the present invention relates to an inductor formed with insulator slots inside, and a method for forming such an inductor
2. Description of Related Art
Inductor is widely used for radio frequency (RF) application. The application covers a very broad spectrum. Some applications, such as personal handy-phone system (PHS), require an inductor to work with frequencies below 1 GHz. Accordingly, the maximum quality factor (abbreviated as Q hereinafter) of the inductor has to move into the sub-GHz range.
For an inductor to have acceptable inductance and maximum quality factor below 1 GHz, a conventional solution is stacking metal layers in parallel. However, this solution increases sidewall capacitance coupling and consequently degrades the broadband performance of the quality factor. Another solution is widening the coil of the inductor, but an over-wide coil tends to violate chemical-mechanical polishing (CMP) rules. In addition, although widening the coil lowers the resistance and improves the maximum quality factor, it also significantly accentuates the variation in the fabrication process.
The maximum quality factor of an inductor should be as high as possible. Therefore it is desirable to have an inductor which works properly with a frequency less than 1 GHz and is without the drawbacks of conventional solutions.